The present invention relates generally to processing of semiconductor devices, and specifically to methods and apparatus for removal of foreign particles and contaminants from solid-state surfaces.
Removal of particles and contaminants from solid state surfaces is a major problem in integrated circuit manufacture. Integrated circuit manufacture includes, but is not limited to, production of semiconductor wafers, printed circuit boards, component packaging, and the like. As the trend to miniaturize electronic devices and components continues, and critical dimensions of circuit features become ever smaller, the presence of even a minute foreign particle on a substrate wafer during processing can cause a fatal defect in the circuit. Similar concerns affect other elements used in the manufacturing process, such as masks and reticules.
Various methods are known in the art for stripping and cleaning foreign matter from the surfaces of wafers and masks, while avoiding damage to the surfaces themselves. For example, U.S. Pat. No. 4,980,536 to Asch et. al. which is incorporated herein by reference, describes a method and apparatus for removal of particles from solid-state surfaces by laser bombardment. U.S. Pat. Nos. 5,099,557 and 5,024,968 to Engelsberg, which are also incorporated herein by reference, describe methods and apparatus for removing surface contaminants from a substrate by high-energy irradiation. The substrate is irradiated by a laser with sufficient energy to release the particles, while an inert gas flows across the wafer surface to carry away the released particles.
U.S. Pat. No. 4,987,286 to Allen, which is likewise incorporated herein by reference, describes a method and apparatus for removing minute particles (even sub-micron particles) from a surface to which they are adhered. An energy transfer medium, typically a fluid, is interposed between each particle to be removed and the surface. The medium is irradiated with laser energy, and absorbs sufficient energy to cause explosive evaporation, thereby dislodging the particles.
U.S. Pat. No. 5,023,424 to Vaught, which is incorporated herein by reference, describes a method and apparatus for using laser-induced shock waves to dislodge particles from a wafer surface. A particle detector is used to locate the positions of particles on the wafer surface. A laser beam is then focused at a point above the wafer surface near the position of each of the particles, in order to produce gas-borne shock waves with peak pressure gradients sufficient to dislodge and remove the particles. U.S. Pat. No. 5,023,424 further notes that immersion of the surface in a liquid (as in the above-mentioned U.S. Pat. No. 4,987,286, for example) is unsuitable for use in removing small numbers of microscopic particles.
Removal of small particles can also potentially damage the substrate. Generally, it has been found that sub-micron particles are the most difficult to detect and remove. Shock waves may cause these particles to explode by either splitting in a few pieces or to xe2x80x9csplashxe2x80x9d into a large number of fragments. There is a need to find a process which can be used to clean integrated circuits, without adding contaminants, without damaging the substrate surface upon explosion of a particle, and yet with removing particles, or fragments thereof, of different contaminants and of a large range of sizes.
It is an object of some aspects of the present invention to provide improved methods and apparatus for efficient removal of contaminants from solid-state surfaces.
It is a further object of some aspects of the present invention to provide improved methods and apparatus for removal of microscopic particles on semiconductor wafers and on other elements used in semiconductor device production.
In preferred embodiments of the present invention, a system for removing a particle from a solid-state surface, such as a semiconductor wafer, comprises a fluid delivery unit and a suction module. The fluid delivery unit deposits a fluid, preferably a vapor or a spray, onto the surface. Generally, the fluid condenses on particles on the surface, so that the overall size and mass of the particles with the liquid around them are much larger than they were before. When the suction module is actuated, a turbulent mass-transfer regime surrounding the particle induced by the suction force introduces a mechanical shock to the particle. The mechanical shock, coupled with the dissolution forces of the particle into the liquid phase, tends to release the particle from the surface. The suction force enables the particle and the liquid to be removed from the surface.
Thus, the inventors have found that wetting the surface prior to applying suction provides more effective removal of microscopic particles than does suction alone. This result contrasts with suction-based particle removal systems known in the art, in which suction is applied to a dry surface. While moisture may make it more difficult to remove large particles from the surface, it increases the effectiveness of the suction in mobilizing very small particles, particularly particles below approximately 1 micron, whose small size and mass makes it otherwise difficult to remove them.
In some preferred embodiments of the present invention the system is constructed such that the fluid is delivered in a channel and the suction forces remove the particle and fluid in another channel. The channels are typically constructed to be perpendicular to the solid-state surface. Preferably, the fluid is delivered in an inner channel, and the suction force is applied in an outer annular channel. Further preferably, the outer channel has a narrow gap (radius of outer channel less radius of inner channel) of less than 1 mm, and most preferably of around 0.3 mm. The nozzle edge of both of the channels is placed approximately 0.1-0.5 mm above the solid-state surface, and most preferably about 0.2 mm above the solid-state surface.
In further preferred embodiments of the present invention the system is constructed with a vaporizer which vaporizes the fluid phase. Typically, the vaporizer comprises at least one heating element, which is configured to heat both the fluid delivery channel and suction channel concomitantly.
In preferred embodiments of the present invention, improved methods and apparatus are provided for particle removal from a surface in which the fluid phase comprises water, or water vapor. The fluid phase is typically heated to 30-80xc2x0 C. When the heated fluid impacts on the solid-state surface, some or all of the fluid molecules condense on the surface.
In some aspects of preferred embodiments of the present invention, a method and system are provided for delivering the fluid phase to the solid-state surface, wherein the delivery of the fluid phase is stopped and a suction force for particle removal is applied after waiting for a time period. This has been shown experimentally to be the most effective regime for particle removal.
In further preferred embodiments of the present invention, a turbulent flow regime is introduced by means of a combination of the fluid flow and the suction forces. The flow regime at solid-state surface is such that the horizontal fluid velocity immediately above the surface and parallel thereto is at least 100 m/s and is preferably around the speed of sound (around 330 m/s). The flow regime above the surface substantially reduces or eliminates boundary layer phenomena, stagnation and laminar flow phenomena.
In some other aspects of preferred embodiments of the present invention, the system is integrated with a laser cleaning tool. The tool is typically configured to apply laser energy to the surface so as to aid in the release of the particles from the surface. The inventors have also found that condensation-based suction is effective in removing most of the particles that tend to explode during the laser cleaning process, and thus, it is useful to integrate these two methods (suction cleaning and laser cleaning).
In some aspects of preferred embodiments of the present invention, a method and system are provided for delivering the fluid phase so as to substantially reduce or eliminate particle explosion phenomena. The need, in turn, to remove particle fragments is thus reduced or eliminated. Thus, this system provides efficient particle removal, substantially without damage to the wafer or other solid-state surface.
There is thus provided in accordance with a preferred embodiment of the present invention a method for removing particles from a surface, including:
applying a fluid to the surface on which the particles are distributed, wherein at least some of the particles have a dimension of less than approximately one micron, so as to coat the particles with the fluid, and
applying a suction force in a vicinity of the surface after applying the fluid so as to remove from the surface a majority of the at least some of the particles having the dimension of less than approximately one micron.
Preferably, the fluid includes water. Further preferably, applying the fluid includes using a carrier gas to convey the fluid to the surface. Additionally, applying the fluid preferably includes heating the fluid that is applied to the surface. Further preferably, heating the fluid includes heating the fluid to 30-80xc2x0 C.
In a preferred embodiment, applying the suction force includes waiting for a predetermined time period following applying the fluid before applying the suction force. Preferably, the time period is in the range of 0.01 to 2 seconds. Further preferably, applying the fluid includes applying the fluid through a channel held approximately perpendicularly to the surface.
In a preferred embodiment, applying the suction force includes applying the suction force through an annular channel surrounding the channel through which the fluid is applied. Further preferably, applying the suction force further includes heating the annular channel and the fluid delivery channel. Yet further preferably, applying the suction force includes applying the suction force through a channel held at a tilt of 1-40 degrees from a perpendicular angle to the surface.
In another preferred embodiment, applying the suction includes applying the suction so as to generate a turbulent flow regime at the surface. Preferably applying the suction force includes applying the suction force for a period of time between 0.1 and 10 seconds. Further preferably, at least some of the particles removed have a dimension less than 0.2 micron.
In yet another preferred embodiment, applying the suction includes removing the particles via a nozzle having an aperture of less than 10 mm. Preferably, the aperture is between 0.5 and 5 mm. Further preferably, the nozzle is placed approximately 0.1-0.5 mm above the surface.
In a preferred embodiment, the surface is the surface of a semiconductor wafer.
There is thus provided in accordance with another preferred embodiment of the present invention a method for removing particles from a surface, including:
applying a fluid to the surface on which the particles are distributed so as to coat the particles with the fluid, and
applying a suction force in a vicinity of the surface after applying the fluid so as to generate a horizontal flow velocity of the fluid of at least 100 m/s, thereby removing at least some of the particles.
Preferably, the particles have a dimension of less than one micron.
There is thus provided in accordance with another preferred embodiment of the present invention a method for removing particles from a surface, including:
applying a fluid to the surface on which the particles are distributed, including particles having a dimension of less than approximately one micron, so as to coat the particles with the fluid, and
applying a suction force in a vicinity of the surface after applying the fluid so as to generate a horizontal flow velocity of the fluid of at least 100 m/s, thereby removing at least some of the particles have the dimension of less than approximately one micron.
Preferably, the horizontal flow velocity is in a range of a speed of sound.
There is thus provided in accordance with another preferred embodiment of the present invention, a method of removing a particle from a surface, including:
applying a fluid to the surface so as to coat the particle,
applying a laser beam to the surface such that absorption of the beam at the surface releases the coated particle from the surface substantially without causing the particle to explode, and
removing the released particle and the fluid from the surface by means of a suction force.
There is thus provided in accordance with a preferred embodiment of the present invention, apparatus for removal of particles from a surface, including:
a fluid delivery unit adapted to apply a fluid to the surface on which the particles are distributed, wherein at least some of the particles have a dimension of less than one approximately micron, so as to coat the particles with the fluid, and
a suction unit constructed to apply a suction force to the surface after applying the fluid so as to remove from the surface a majority of the at least some of the particles having the dimension of less than approximately one micron.
Preferably, the apparatus includes a vaporizer, which includes a heating element configured to heat the fluid before it is applied to the surface. Further preferably, the heating element is further configured to heat the particle and fluid during their removal from the surface by the suction unit.
There is thus provided in accordance with another preferred embodiment of the present invention, apparatus for removal of particles from a surface, including:
a fluid delivery unit adapted to apply a fluid to the surface on which the particles are distributed, including particles having a dimension of less than approximately one micron, so as to coat the particles with the fluid, and
a suction unit constructed to apply a suction force in a vicinity of the surface after applying the fluid so as to generate a horizontal flow velocity of the fluid of at least 100 m/s, thereby removing at least some of the particles have the dimension of less than approximately one micron.
There is thus provided in accordance with a preferred embodiment of the present invention, apparatus for removing a particle from a surface, including:
a fluid delivery unit adapted to apply a fluid to the surface so as to coat the particle with the fluid,
a laser delivery unit adapted to apply a laser beam onto the surface such that absorption of the beam at the surface releases the particle substantially without causing the particle to explode, and
a suction unit constructed to apply a suction force to the surface so as to remove the particle and the fluid from the surface.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which: